Browsing by Author "Baranov, A. I."
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Item Deuteron NMR and a Model for Phase Transitions in Monoclinic RbD 2 PO 4 .(1989-02) Jarh, O.; Dolinšek, J.; Topič, B.; Žekš, B.; Blinc, Robert; Schmidt, V. Hugo; Shuvalov, L. A.; Baranov, A. I.The quadrupole-perturbed deuteron NMR spectra and spin-lattice relaxation times of monoclinic RbD2PO4 have been measured and the electric-field-gradient tensors at the deuteron sites have been determined in phase I at 110 °C, phase III at 80 °C, and phase III at 40 °C. The results are incompatible with a location of the D(2) and D(3) deuterons in the center of the corresponding H bonds. They show that these deuterons are disordered between two off-center sites in phases I and II, whereas they are ordered in phases III and IV. A four-sublattice model accounting for all four phase transitions in monoclinic RbD2PO4 is proposed.Item Dielectric anomalies above the glass transition in the mixed K1-x(NH4)xH2PO4 crystals(1992) Baranov, A. I.; Shuvalov, L. A.; Schmidt, V. HugoThe temperature dependences of the complex dielectric constant have been measured in the mixed K1-x(NH4)xH2PO4 crystals at frequencies 10Hz-100kHz. For ammonium concentrations 0.3 ≤ x ≤ 0.6 pronounced dielectric anomalies in c-direction has been detected in the temperature range 200–260K. It was found that in this temperature range the dielectric relaxation dispersion is changed dramatically.Item Influence of NH4-Rb substitution on the phase transitions with different kinds of proton disorder in mixed [(NH4)1-xRbx]3H(SO4)2 crystals(1998-09) Baranov, A. I.; Dolbinina, V. V.; Yakushkin, E. D.; Vinnichenko, Yu. V.; Schmidt, V. Hugo; Lanceros-Mendez, S.The role of ammonium ions in order–disorder ferroelastic, ferroelectric and structural phase transitions was studied in mixed [(NH4)1–x Rb x ]3H(SO4)2 0 < x < 1 crystals by dielectric spectroscopy and ac calorimetry. A new superprotonic phase was detected in compounds with x > 0·6. It was found that small Rb concentrations, x < 0·05, strongly smear out the temperature anomalies of dielectric constant and specific heat for phase transitions II–III, III–IV, IV–V and V–VIII. At x > 0·09 these phase transitions are fully suppressed. Finally, for Rb concentrations 0·05 < x < 0·9 a proton glass phase appears below 35 K.Item Phase diagram and dielectric properties of mixed Cs1-x(NH4)xH2PO4 crystals(2002) Baranov, A. I.; Dolbinina, V. V.; Lanceros-Mendez, S.; Schmidt, V. HugoInfluence of NH4 M Cs substitution has been studied in the mixed Cs 1 m x (NH 4 ) x H 2 PO 4 crystals system by means of dielectric measurements. The x-T phase diagram was determined: for ammonium concentrations up to 0.1 the system has a monoclinic paraelectric phase with a transition into a ferroelectric phase whose temperature increases with increasing ammonium concentration. For ammonium concentration 0.4 to 1.0 the system shows a tetragonal paraelectric phase and a transition into an antiferroelectric phase. No solid solutions with concentrations between 0.1 and 0.4 could be grown. The system was further studied with the quasi-one-dimensional Ising model and the three-dimensional anisotropic Ising model.